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    Lewis and Clark lunars: more 1803 Almanac data
    From: George Huxtable
    Date: 2004 Apr 16, 17:33 +0100

    Has anyone else, I wonder, been struggling to resolve that doubtful
    lunar-distance observation made on the night of December 2-3, 1803, beside
    Bruce Stark, Mike Burkes, and me? So far, it seems clear that L&C must have
    made some big error(s), but we have not been able to establish what they
    are. Maybe they have misidentified some other star as Aldebaran. Rigel
    gives a much closer answer, but still not close enough. I have eliminated
    any of the four planets, which weren't near the right place at that time.
    
    The original message defining the problem was sent on 8 April, under the
    threadname "Lewis and Clark lunars: a request for help".
    
    It was followed up by some relevant information copied from the 1803
    almanac in two mailings on 12 April.
    
    Now, with Bruce Stark's help, for which I'm grateful, I can add a bit more
    data from the 1803 almanac, giving Moon's semidiameter and Horizontal
    Parallax at some relevant times.
    
    
    Here is the 1803 Almanac data:
    
    Dec. 2nd. Midnight: SD 15' 38", HP 57' 21"
    
    Dec. 3d.   Noon: SD 15' 31", HP 56' 55"
    
    Dec. 3d. Midnight: SD 15' 23", HP 56' 29"
    
    =======================================
    
    If anyone else feels the need for further information from that almanac,
    I'm sure that Bruce and I, between us, can supply it.
    
    Below, copied once again below, is that star data and almanac data from
    around the time of that lunar distance observation, as previously posted on
    8 April. Sorry all this necessary information been posted bit by bit.
    
    Yours, George.
    
    ===========================================================
    
    With the data from the 1803 almanac (copied again below), I forgot to
    include positions for Aldebaran and Regulus.
    
    These weren't taken from the 1803 almanac (I don't think star data was
    included in the almanac then) but were instead extrapolated backwards by 60
    years, to the start of 1804, from an 1864 almanac that I have. They agree
    with predictions (with rates of change) extrapolated forward from 1765,
    from the first edition of Maskelyne's "British Mariner's Guide".
    
    Unlike the star positions in a modern almanac, which are provided at 3-day
    intervals to 0.1 arc-minutes, these are only mean positions of stars,
    allowing for precession and (where applicable) proper motion, but
    neglecting aberration and nutation. As a result, they are only good to the
    nearest 0.5 arc-minutes or so.
    
    Aldebaran. Right Ascension  66deg 10.3' or 4h 24m 41s; Declination N16deg 06.3'
    Regulus.   Right Ascension 149deg 28.8' or 9h 57m 55s; Declination N12deg 55.2'
    
    Below, that earlier message is repeated.
    =========================
    
    Relevant to those 1803 lunar distances by Lewis and Clark.
    
    I can quite some relevant extracts from the 1803 Nautical Almanac that I
    jotted down at my last library visit-
    
    Astronomical times and dates, of course, starting at noon each day, 12
    hours after the start of the civil day with the same name and date.
    .
    All times Greenwich Apparent time.
    
    Sun
                     RA             Dec        EOT (sub)
    2 Dec noon  16h 30m 54.1s  S21deg 53' 08"  10m 33.7s
    3 Dec noon  16h 35m 13.9s  S22deg 02' 07"  10m 10.5s
    
    Moon
                      RA
    2 Dec midnight 127deg 24'  20deg 05'
    3 Dec noon     133deg 54'  17deg 50'
    3 Dec midnight 140deg 08'  15deg 25'
    
    Lunar distances.
                    Aldebaran West   Regulus East    Sun East
    2 Dec midnight   58deg 00' 46"  22deg 19' 53"
          XV hrs     59deg 37' 27"  20deg 41' 16"
       XVIII hrs     61deg 13' 48"  19deg 03' 06"
         XXI hrs     62deg 49' 50"  17deg 25' 23"  120deg 36' 21"
    3 Dec  noon      64deg 25' 31"  15deg 48' 08"  119deg 06' 46"
         III hrs     66deg 00' 52"                 117deg 37' 33"
    
    No doubt you're aware that EOT (Equation of Time) was then defined in the
    opposite way than we do it now.
    
    If there's anything else that anyone would find useful, I will note it down
    at my next visit.
    
    George.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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